[Navy Lifer]

wouldn't 275/40 be way too small a diameter?...285/45 will give the exact same diameter as stock tires...that's what i'm looking at

do you think a 285/45/17 tire on a 9.5" wide, 4.5" bs wheel fit in the rear?...or would i need to go 5" bs?...looking to push it out as far as I can to stay flush, but avoid rubbing...I guess I can roll the fenders too

Well, there have been more than a few who have used "inappropriate" tires on their cars--tire load rating is something that not many pay attention to these days, it seems. A "too small" tire, in diameter, is a conscious choice, right or wrong--but you are correct, in my view.

Wheel bead width becomes more critical as tire aspect ratio is reduced, so the 275/40-17 tire may fit a stock SS wheel, but it is pinching the sidewalls more than the tire manufacturer intended.

If a 275/45 or 285/45 option existed, yes, they would be far better--as to your wheel question, a 9.5" wheel is going to be 10.5" wide, so 4.5" BS means there will be 6" of wheel outboard of the hub flange plane. A stock Impala SS wheel (5.06" BS) has about 4.5" of wheel outboard of the hub flange plane--can the body handle an extra 1.5" of wheel in that direction? I doubt it. I'm not comfortable even with a 9.5" wheel with 5" BS....5.5" BS would be safe, but still depends on tire size selected.

As I suggested earlier, "too much" backspace can be corrected with a proper spacer/wheel stud setup, but if there is NOT enough wheel BS, it is not normally possible to remove material from the wheel mounting pad to pull it inward.

Where someone wants to really have the ability to stuff a wide wheel/tire into a B-body sedan, my first suggestion would be to use the narrow housing if the car doesn't already have it.

This might be a dumb question but does the overall diameter effect offset/backspacing or just the width.

Offset/backspacing is a wheel dimension calculation. Tires only impact this when the size selection is going to cause a rub or the wheel is too narrow or too wide for the tire selected--based on manufacturer recommended wheel width.

 

[STUpid B00ST]

Sorry bill I should of worded that better. I was meaning the wheel diameter ie 15" 16" 17".

 

[Navy Lifer]

The tire doesn't care, as long as the wheel & tire are compatible (bead width vs specs for tire size)--wheel offset/BS simply dictates the position of the wheel/tire assembly laterally.

 

[STUpid B00ST]

Ok thanks bill

 

[Firewood]

I have some direct roadmaster experience. Back when I ran a wheel shop I put an 18x8.5 wheel with a 255/45R18 under a RMS and it was a perfect fit with a 0 offset.
However pushing up to 275 with tire is a bit in the unknown zone. I know from experience a 17x9.5 Torque Thrust II with 5.5 backspacing fits an SS FRONT AND REAR like a glove with a 255/50 tire, and have little worry about the same on an RMS.

 

[STUpid B00ST]

Thanks Firewood for the input. It's good to here you can fit a wide wheel up front. And when they he time comes I'll probably go with 255's, but it would be cool to see that 275 all around.